1. Field of the Invention
The present invention relates to a semiconductor device, which may be used as, for example, a semiconductor rectifying element having a constant reverse breakdown voltage such as a voltage regulator diode (Zener diode), and a manufacturing method thereof.
2. Description of the Related Art
A voltage regulator diode 1 as shown in FIG. 1 is known. The semiconductor diode (hereinafter referred as “an earlier semiconductor diode”) 1 has the simple three-layer structure embracing, for example, n-type semiconductor layer 2 of high impurity concentration, n-type semiconductor layer 3 and p-type semiconductor layer 4 of high impurity concentration, formed in silicon substrate. And, metal films 5,6 which respectively serves as the ohmic electrodes have been deposited on the top surface of n-type semiconductor layers 2 and on the bottom surface of p-type semiconductor layers 4.
Generally, in a chip outer-surface, at which the termination of pn junction, implemented in the earlier semiconductor diode with such stacked geometry, is exposed, a high electric field is induced along the depletion layer of pn junction between which the reverse-bias voltage was applied. However, by receiving the effect of impurity elements and ions adsorbed on the surface, etc., the electric field at the outer-surface is further intensified locally, and the breakdown phenomena become frequent. Therefore, the reverse breakdown voltage theoretically expected is not obtained in the earlier semiconductor diode. Then, the appropriate bevel structure is adopted in order to reduce the electric field at the chip outer-surface, by cutting obliquely the outer-surface of the earlier semiconductor diode 1, where the pn junction interface is exposed. By adopting such bevel contour, the electric field at the chip outer-surface 7 is reduced, and the breakdowns are designed to occur along whole junction interface contained inside of the semiconductor chip, attempting the stabilization of the breakdown behavior. Still, the fact that breakdown voltage is also improved further by adopting the bevel structure in power semiconductor devices having higher maximum operating voltages than the voltage regulator diode such as the Zener diode is well known.